1. Field of the Invention
The present invention relates generally to a weather-resistive barrier for a roofing structure, and specifically to a reinforced roof underlayment having an improved strength and durability to provide a waterproof layer resistive to deterioration from external elements.
2. Description of Related Art
Roofing structures for buildings typically include an underlayment positioned between a roof support deck and an overlayment. The overlayment, such as asphalt shingles, tiles, wooden shakes, slate tiles, metal roofing, or the like, is intended to provide protection from external weather conditions like wind, rainwater, and snowmelt. In order to further protect against moisture and other elements which may pass under the overlayment, the underlayment is installed over the roof deck and under the overlayment to provide an added waterproof barrier. The additional moisture protection provided by the underlayment is particularly necessary with tile roofs, where gaps often exist between the tiles where moisture can pass through. The underlayment also serves the function of providing a seal around roofing fasteners used to affix the tiles to the roof support deck.
Underlayments have conventionally been produced by coating a layer of organic paper with a certain density of asphalt. Over time, the underlayment is exposed to moisture and other external elements which gather underneath the overlayment. This exposure to external elements causes the organic paper-based underlayments to weather and deteriorate over time, especially in tile roofs where gaps between the tiles can expose the underlayment to larger amounts of external elements. Furthermore, constant exposure to sunlight coupled with heat rising from within the building often results in the roofing structure being exposed to high temperatures which can dry out and further deteriorate the underlayment. The deterioration of the underlayment allows moisture to pass through the underlayment and leak through the roof structure, resulting in damage to the interior of the building. The integrity of the roof structure is often dependent upon the very effectiveness of the underlayment. In attempting to utilize existing organic paper-based underlayments in tile roofs, it has been found that the underlayments deteriorate much more quickly than the tile overlayment. Thus, the effectiveness of the waterproof barrier provided by the roofing structure is often limited to the life of the underlayment.
Another problem with existing underlayments being formed from an organic, paper-based material is that the underlayments are flexible and require a solid support structure beneath them. When these organic paper-based underlayments are used with spaced support structures, such as spaced rafters, the underlayments will drape between the rafters to which the underlayment is attached. When moisture gathers underneath the overlayment, it will tend to congregate in the draped portions of the underlayrnent between the rafters. This moisture creates tension on the underlayment in the draped portions as well as the points on underlayment where it is attached to the rafters, where it has been found that the organic paper-based underlayments tend to tear when the tension becomes too great in these locations from excess moisture accumulating. The resistance of the underlayment to tearing is further weakened by the above-described deterioration of the underlayment over time. Thus, organic underlayments have been found to be ineffective in providing a waterproof barrier when used with non-solid support structures.
There is a clearly need for a roofing underlayment having an improved resistance to deterioration from exposure to external elements. Moreover, there is a need for a tear-resistant roofing underlayment having an improved longevity which closely matches that of the overlayment.